In recent years, with progress of the information society, biometric technologies for confirming the personal identity based on personal physical characteristics have been put into practical use as security technologies for preventing illegal use of bank cards and electronic money. Among biometric technologies such as those utilizing palmar veins and voiceprints, a fingerprint authentification technology using fingerprints has been considerably studied so far.
For example, in Japanese Laid-open Patent Publication No. 61-221883, a fingerprint is irradiated with light and optically checked by light reflected from the fingerprint.
In Japanese Laid-open Patent Publication No. 05-61965, a pressure difference caused by irregularities of a fingerprint is read by a piezoelectric thin film, whereby checking is performed.
In Japanese Laid-open Patent Publication No. 07-168930, checking is performed based on change in resistance or capacitance of a pressure-sensitive sheet, the change being caused when a skin is contacted with the pressure-sensitive sheet.
However, among these techniques, the technique in Japanese Laid-open Patent Publication No. 61-221883 which uses the optical method has disadvantages that the technique is not suitable for reduction in size, and is not possible to be used for general purpose, thereby being limited in usage. The technique in Japanese Laid-open Patent Publication No. 07-168930 has difficulty in practical use, because of use of the pressure-sensitive sheet that is made of a special material and is unworkable.
As a technique for solving these problems, Japanese Laid-open Patent Publication No. 2003-269907 discloses a capacitance type fingerprint sensor (surface profile sensor) formed on a semiconductor substrate. In the fingerprint sensor, a plurality of detection electrode films formed on the semiconductor substrate in an array face a skin, and each of the detection electrode films and the skin function as electrodes in a capacitor. The distance between the electrodes in the capacitor varies depending on the irregularities on a fingerprint. Accordingly, an image of the fingerprint is obtained by allowing each of the detection electrode films to act as one pixel, and sensing and visualizing the capacitance of each capacitor. Compared to the sensor according to the optical method, the fingerprint sensor according to this method requires no special interface and can be reduced in size.
In addition to those described above, Japanese Patent Translation Publications Nos. 2000-512053, 2002-544380, 2001-506319 and 2003-534223; Japanese Laid-open Patent Publications Nos. 2004-218087, 2004-256837, 2003-58872, 2002-294470, 2002-194123, and 2003-301257; Japanese Patents Nos. 3624843 and 3658342; and U.S. Pat. Nos. 6,261,693, 5,858,477 and 6143142 also disclose techniques relating to the embodiments.